It says something about the pass-first, offense-led nature of the modern NFL, that three of the five assistant coaches on this list are offensive coordinators.

Even a decade ago, defensive coordinators were usually considered better head coach material. However, now most teams want coaches expert at scheming points, rather than denying them.

These five assistants are all young coaches, fast developing reputations for excellence on their particular side of the ball. Those reputations could soon lead to head coaching gigs.

Mike McCoy, Offensive Coordinator, Denver Broncos

What brings Denver Broncos offensive coordinator Mike McCoy to the attention, is how the 40-year-old has managed to successfully direct two very different schemes and personnel.

Last season, McCoy called the plays for an offense led by Tim Tebow. It was a heavy-run system, featuring plenty of read option calls, designed to get Tebow out of the pocket and on the move.

Fast forward one year later and McCoy was given Peyton Manning and his fast-paced, hurry up offense. It's a pass-first scheme featuring multiple route combinations for receivers.

That's a night and day difference from the style implemented to suit Tebow. Yet McCoy has done excellent work ensuring a smooth transition for his players.

Scheme flexible and quarterback-friendly, McCoy's stock will continue to rise, the more Manning dominates.

Kevin Coyle, Defensive Coordinator, Miami Dolphins

In his first season as a coordinator at the pro level, former Cincinnati Bengals secondary coach Kevin Coyle has fashioned a tough defense with the Miami Dolphins.

Coyle has successfully engineered a switch from a 3-4 to a 4-3 base front, not an easy schematic shift. Players like defensive linemen Paul Soliai and Randy Starks, who were thought to be suitable only in a 3-4, are thriving in Coyle's scheme.

The Dolphins currently own the NFL's third stingiest defense in points and are also ranked third against the run. As well as rookie quarterback Ryan Tannehill has played, it is Coyle's defense that has keyed Miami's 4-3 start.

Jay Gruden, Offensive Coordinator, Cincinnati Bengals

45-year-old Jay Gruden continues to call an excellent scheme for the Cincinnati Bengals' young offense. In 2011, Gruden helped make instant stars out of rookie pair quarterback Andy Dalton and wide receiver A.J. Green.

That was enough to make Gruden a hot commodity in coaching circles and he has continued in that vein for most of this season. He consistently designs ways to free Green deep against regular double coverage.

Gruden has also shown a knack for catching opponents off guard with the trick play. He has used the Wildcat package to outwit more than one defense, just as he did in Week 4 against the Washington Redskins.

Ray Horton, Defensive Coordinator, Arizona Cardinals

The Arizona Cardinals have collapsed following their fast start to the campaign, but the problem has not been Ray Horton's defense. The 52-year-old was hired last season to finally create a credible, Pittsburgh Steelers-style, zone blitz 3-4 scheme in Arizona.

His unit finished his first year in strong fashion and things have been even better this season. Horton is producing star turns from players like defensive end Calais Campbell and inside linebacker Daryl Washington.

Horton's blitz schemes are the most impressive element of his play calling. He designs intricate, multiple blitzes, that free rushers and combine heavy pressure with deceptive coverage looks. These clever schemes have helped the Cardinals lead the league in sacks with 26 and rank sixth overall in total defense.

Horton has an excellent understanding of a defensive scheme that is the envy of most of the NFL. That makes him an excellent candidate to be offered the chance to run his own team in the near future.

Greg Roman, Offensive Coordinator, San Francisco 49ers

Greg Roman continues to gather fans and plaudits for his work with the San Francisco 49ers' functional but effective offense. Roman operates a run-first attack, playing to the strengths of star running back Frank Gore.

What's most impressive is the many ways Roman is prepared to use his personnel. His heavy-run fronts, featuring two tight ends and up to seven offensive linemen, are being copied by many around the league.

His reputation also grows thanks to the way his system enables otherwise unremarkable quarterback Alex Smith, to protect the ball and make big plays. Smith is the NFL's fourth highest-rated passer and much of that is down to Roman's scheming.

Any team with a struggling quarterback or a youngster who needs to be developed, is sure to consider the 40-year-old a viable head coaching candidate this offseason.